I am still keeping my fingers that Comet C/2013 A1 strikes Mars next year. Not only would it be an amazing show, I can say things like "Not only did curiosity kill the cat, a comet killed the Curiosity."

For example, the path's aphelion might overlap a location, 2½ a.u. from the Sun, at which there's a strong orbital resonance with Jupiter. In that case, gravitational perturbations by the giant planet could have yanked the object out of a nearly circular orbit and onto its eventual collision course with Earth.

xalres:For example, the path's aphelion might overlap a location, 2½ a.u. from the Sun, at which there's a strong orbital resonance with Jupiter. In that case, gravitational perturbations by the giant planet could have yanked the object out of a nearly circular orbit and onto its eventual collision course with Earth.

Snarfangel:I am still keeping my fingers that Comet C/2013 A1 strikes Mars next year. Not only would it be an amazing show, I can say things like "Not only did curiosity kill the cat, a comet killed the Curiosity."

I too kind'a hope it hits the Red Planet, but for selfish scientific purposes. Seeing what it does to Mars might just get Earth to get off its collective ass and get serious about putting our eggs in some more baskets, so to speak. We humans are only one good smack from having this noble experiment terminated.

Crunch61:xalres: For example, the path's aphelion might overlap a location, 2½ a.u. from the Sun, at which there's a strong orbital resonance with Jupiter. In that case, gravitational perturbations by the giant planet could have yanked the object out of a nearly circular orbit and onto its eventual collision course with Earth.

DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy. It did punch a multi-hundred-km long hole in the atmosphere at way-hypersonic speed, which launched a cylindrical shock wave that blasted a pretty significant overpressure over a huge region... rather like an explosion would've... but the rock itself didn't detonate like a nuke or bunker buster or Ron Jeremy does.

EddyKilowatt:DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy. It did punch a multi-hundred-km long hole in the atmosphere at way-hypersonic speed, which launched a cylindrical shock wave that blasted a pretty significant overpressure over a huge region... rather like an explosion would've... but the rock itself didn't detonate like a nuke or bunker buster or Ron Jeremy does.

I'd go with saying it exploded in the same way Columbia exploded. More of a rapid disintegration than explosion.

EddyKilowatt:DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy.

How about those parts of the video where it suddenly flashes brighter than the sun, splits into pieces, and comes down as a shower of small chunks? I agree that it was a more gradual process than a nuclear detonation, but it still dumped a large fraction of its energy in a hurry once it hit denser atmosphere. It was more than just a sonic boom.

Ivo Shandor:EddyKilowatt: DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy.

How about those parts of the video where it suddenly flashes brighter than the sun, splits into pieces, and comes down as a shower of small chunks? I agree that it was a more gradual process than a nuclear detonation, but it still dumped a large fraction of its energy in a hurry once it hit denser atmosphere. It was more than just a sonic boom.

Well okay, sure, there was flaring and disintegration and breakup going on. But all the pieces kept going (at least in the videos linked) in the same general direction. I'm going to maintain that an explosion, at least in the popular understanding of the term, is more like what (professional, civic-scale) fireworks do: a long skinny trail of sparks, followed by a sudden blast, leaving a spherical cloud of sparkly fragments.

But it's obviously a shades-of-gray scale that runs from "slow ablation" through "flaring" and winds up at "detonation", and this rock undoubtedly occupied several spots on that scale at various points during its entry.

EddyKilowatt:Ivo Shandor: EddyKilowatt: DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy.

How about those parts of the video where it suddenly flashes brighter than the sun, splits into pieces, and comes down as a shower of small chunks? I agree that it was a more gradual process than a nuclear detonation, but it still dumped a large fraction of its energy in a hurry once it hit denser atmosphere. It was more than just a sonic boom.

Well okay, sure, there was flaring and disintegration and breakup going on. But all the pieces kept going (at least in the videos linked) in the same general direction. I'm going to maintain that an explosion, at least in the popular understanding of the term, is more like what (professional, civic-scale) fireworks do: a long skinny trail of sparks, followed by a sudden blast, leaving a spherical cloud of sparkly fragments.

But it's obviously a shades-of-gray scale that runs from "slow ablation" through "flaring" and winds up at "detonation", and this rock undoubtedly occupied several spots on that scale at various points during its entry.

I don't think it was ever at conflagration as it was probably always supersonic to impact. I base my proof for that on unicorn to leprechaun ratios.

Ivo Shandor:EddyKilowatt: DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy.

How about those parts of the video where it suddenly flashes brighter than the sun, splits into pieces, and comes down as a shower of small chunks? I agree that it was a more gradual process than a nuclear detonation, but it still dumped a large fraction of its energy in a hurry once it hit denser atmosphere. It was more than just a sonic boom.

Kinetic Energy = 0.5 x mass x velocity squared.

10 tonne meteor at 10 miles per second = nuke-sized boom as it slows to a halt. Might be in the air; as one lump or many; or on the ground. Same energy in all cases - same size boom.

In this case, it disintegrated in the air and the pieces more or less came to a halt. The air friction heats the meteor fragments to several million degrees - so they vaporise and a meteor-vapour cloud expands with great force.

(Which is near as dammit what a nuclear device does - it just sources its energy elsewhere.)

EddyKilowatt:DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy. It did punch a multi-hundred-km long hole in the atmosphere at way-hypersonic speed, which launched a cylindrical shock wave that blasted a pretty significant overpressure over a huge region... rather like an explosion would've... but the rock itself didn't detonate like a nuke or bunker buster or Ron Jeremy does.

wxboy:I'd go with saying it exploded in the same way Columbia exploded. More of a rapid disintegration than explosion.

EddyKilowatt: "I'm going to maintain that an explosion, at least in the popular understanding of the term, is more like what (professional, civic-scale) fireworks do: a long skinny trail of sparks, followed by a sudden blast, leaving a spherical cloud of sparkly fragments."

What you're advocating is that we stop calling red red, because some blind guy thinks it's green.

Due conservation of momentum the "popular understanding" would be an impossible natural event. (The meteor would have to explode with more energy than it carried into the atmosphere to begin with, to have its debris cloud fly substantially free of the original trajectory.) This is one of those cases where the "popular understanding" is more accurately a "popular misconception". And there's no good reason to define words based on the (mis)understanding of people who demonstrably do not know what the fark they're talking about.

Snarfangel:I am still keeping my fingers that Comet C/2013 A1 strikes Mars next year. Not only would it be an amazing show, I can say things like "Not only did curiosity kill the cat, a comet killed the Curiosity."

I read an article which suggested at its size and current speed it might release as much 2x10^10 megatons of energy on impact. That would be the equivalent of 400 million Tsar Bombas (the largest nuke ever detonated at 50+ megatons).

Supersonic jets can easily break windows on the ground, and if one cared to, could do it all along a hundred-mile corridor. They don't do it by exploding, they do it by pushing through the air faster than the air can get out of the way. Result, shockwave, effect, loud boom and broken windows.

You can do an equivalent thing by throwing a rock into a pond at a shallow grazing angle. Rock doesn't explode, it just transfers its energy into a wavefront that spreads outward. If you throw hard enough, maybe the rock breaks up from the forces... it still generates the wave, and the wave is what carries the energy away. Not the rock exploding.

Supersonic jets can easily break windows on the ground, and if one cared to, could do it all along a hundred-mile corridor. They don't do it by exploding, they do it by pushing through the air faster than the air can get out of the way. Result, shockwave, effect, loud boom and broken windows.

You can do an equivalent thing by throwing a rock into a pond at a shallow grazing angle. Rock doesn't explode, it just transfers its energy into a wavefront that spreads outward. If you throw hard enough, maybe the rock breaks up from the forces... it still generates the wave, and the wave is what carries the energy away. Not the rock exploding.

It exploded. Explosions go boom. There is evidence meteors "explode". End of story.

Supersonic jets can easily break windows on the ground, and if one cared to, could do it all along a hundred-mile corridor. They don't do it by exploding, they do it by pushing through the air faster than the air can get out of the way. Result, shockwave, effect, loud boom and broken windows.

You can do an equivalent thing by throwing a rock into a pond at a shallow grazing angle. Rock doesn't explode, it just transfers its energy into a wavefront that spreads outward. If you throw hard enough, maybe the rock breaks up from the forces... it still generates the wave, and the wave is what carries the energy away. Not the rock exploding.

And just to more clear, meteors explode because of heat. Explosions cause shockwaves.

EddyKillowatt: "Supersonic jets can easily break windows on the ground, and if one cared to, could do it all along a hundred-mile corridor. They don't do it by exploding, they do it by pushing through the air faster than the air can get out of the way. Result, shockwave, effect, loud boom and broken windows."

And yet if a supersonic jet did explode, the debris would largely continue along the same trajectory -- looking nothing like the popular conception of a debris cloud -- and though the windows would still have been blown out by the shockwave of its supersonic(-but-likely-not-for-long) passage through the atmosphere, the jet *will still have exploded*.

Supersonic jets can easily break windows on the ground, and if one cared to, could do it all along a hundred-mile corridor. They don't do it by exploding, they do it by pushing through the air faster than the air can get out of the way. Result, shockwave, effect, loud boom and broken windows.

Actually it was the explosion.

According to Phil Plait, at least:UPDATE (23:00 UTC) After looking through more footage, it's become clear that the multiple booms heard were in fact explosions, and not just shock waves from the meteoroid's passing through the air. In some videos, you can see multiple flashes of light inside the contrail, which are clearly from the rock breaking up and then burning up very rapidly and with intense energy-the very definition of an explosion. Over the course of just a couple of seconds, the large energy of motion of the meteoroid was converted into heat, and this exploded with a yield of several thousand tons of TNT. It goes to show that you need not have an asteroid hit the ground to be dangerous, and in fact the hole in the ice made by the plummeting meteoroid was probably the gentlest thing it did.

Crunch61:xalres: For example, the path's aphelion might overlap a location, 2½ a.u. from the Sun, at which there's a strong orbital resonance with Jupiter. In that case, gravitational perturbations by the giant planet could have yanked the object out of a nearly circular orbit and onto its eventual collision course with Earth.

EddyKilowatt:DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy. It did punch a multi-hundred-km long hole in the atmosphere at way-hypersonic speed, which launched a cylindrical shock wave that blasted a pretty significant overpressure over a huge region... rather like an explosion would've... but the rock itself didn't detonate like a nuke or bunker buster or Ron Jeremy does.

You know, I'm gonna guess that the astronomers who are reporting on the size of the meteor and energy of the explosion are working with a lot more data and expertise than your armchair analysis. Even on the face of it I don't find your explanation particularly plausible. I have my doubts that a sonic boom can create that much overpressure at the ground from 12-15 miles up. A jet flying low can break windows, sure, but not from 70-80,000ft altitude.

EddyKilowatt:Ivo Shandor: EddyKilowatt: DNRTFA, but everyone keeps saying "explosion", and I don't see much evidence that the thing actually, you know, blew up with any significant part of its 500-kiloton energy.

How about those parts of the video where it suddenly flashes brighter than the sun, splits into pieces, and comes down as a shower of small chunks? I agree that it was a more gradual process than a nuclear detonation, but it still dumped a large fraction of its energy in a hurry once it hit denser atmosphere. It was more than just a sonic boom.

Well okay, sure, there was flaring and disintegration and breakup going on. But all the pieces kept going (at least in the videos linked) in the same general direction. I'm going to maintain that an explosion, at least in the popular understanding of the term, is more like what (professional, civic-scale) fireworks do: a long skinny trail of sparks, followed by a sudden blast, leaving a spherical cloud of sparkly fragments.

But it's obviously a shades-of-gray scale that runs from "slow ablation" through "flaring" and winds up at "detonation", and this rock undoubtedly occupied several spots on that scale at various points during its entry.

Ever see what a claymore does? Is that an explosion, or a slow burn with some flaring? I would have to say that based on the multiple flares coupled with the corresponding BOOM's recorded at the same time that there were several explosions, with the whole group getting spread out while still traveling in pretty much the same direction.